The influence of temperature,humidity,atmospheric pressure,visibility,atmospheric path and other meteorological conditions on atmospheric transmittance is calculated by Lowtran. According to the analysis,when the temperature rises from 10℃ to 20℃,the atmospheric transmittance of medium wave bands and long wave bands decreases by 20.6% and 61.5% respectively；the humidity increases from 30% to 50%,atmospheric transmittance of medium wave bands and long wave bands decreases 26.6% and 75.3% respectively；the visibility decreases from 14km to 8km,atmospheric transmittance in medium wave and long wave bands decreases 65.2% and 66.7%,respectively. When the visibility is 8km,the atmospheric path increases from 50km to 60km,and the atmospheric transmittance of medium wave bands and long wave bands decreases by 47.7% and 60.0% respectively,indicating that atmospheric conditions significantly affect the atmospheric transmittance,and thus the action range of infrared thermal imager. The ability of medium wave infrared thermal imager to adapt to complex meteorological conditions is better than that of long wave infrared thermal imager.